Integrated CMOS porous sensor

Abstract

A single chip wireless sensor (1) comprises a microcontroller (2) connected by a transmit/receive interface (3) to a wireless antenna (4). The microcontroller (2) is also connected to an 8 kB RAM (5), a USB interface (6), an RS232 interface (8), 64 kB flash memory (9), and a 32 kHz crystal (10). The device (1) senses humidity and temperature, and a humidity sensor (11) is connected by an 18 bit SigmaDelta A-to-D converter (12) to the microcontroller (2) and a temperature sensor (13) is connected by a 12 bit SAR A-to-D converter (14) to the microcontroller (2). The device (1) is an integrated chip manufactured in a single process in which both the electronics and sensor components are manufactured using standard CMOS processing techniques, applied to achieve both electronic and sensing components in an integrated process.

The invention claimed is: 
     
       1. An integrated sensor device comprising:
 MOS circuits in a semiconductor substrate, 
 an interconnect stack comprising at least three interconnect levels, each interconnect level having interconnect conductors and insulating dielectric, said interconnect levels being over the substrate and interconnecting the MOS circuits, 
 a sensor having electrodes embedded in the interconnect dielectric and being integrally formed with the interconnect conductors, a porous material for ingress of gas or humidity being sensed, 
 the MOS circuits including a circuit for processing signals from the sensor electrodes, and 
 at least some of said circuits being located directly beneath the sensor in a vertical dimension. 
 
     
     
       2. The integrated sensor device as claimed in  claim 1 , wherein the sensor material includes a porous oxide interconnect dielectric at least part of which is exposed. 
     
     
       3. The integrated sensor device as claimed in  claim 1 , wherein the sensor material comprises a porous oxide interconnect dielectric, and wherein the porous oxide is carbon-doped SiO 2 . 
     
     
       4. The integrated sensor device as claimed in  claim 1 , wherein the sensor is a capacitive sensor. 
     
     
       5. The integrated sensor device as claimed in  claim 1 , wherein the sensor porous material comprises polyimide. 
     
     
       6. The integrated sensor device as claimed in  claim 5 , wherein the sensor includes a passivation layer over the sensor electrodes. 
     
     
       7. The integrated sensor device as claimed in  claim 5 , wherein the sensor includes a passivation layer over the sensor electrodes, the polyimide is on the passivation layer, and the MOS circuits are adapted to detect changes in a fringe field between the sensor electrodes. 
     
     
       8. The integrated sensor device as claimed in  claim 5 , wherein the sensor includes a reference capacitor beneath the passivation layer. 
     
     
       9. The integrated sensor device as claimed in  claim 5 , wherein the circuits include an analogue-to-digital converter. 
     
     
       10. The integrated sensor device as claimed in  claim 5 , wherein the passivation layer is of Si 3 N 4  composition. 
     
     
       11. The integrated sensor device as claimed in  claim 1 , wherein the sensor porous material includes a porous oxide, and wherein the sensor includes a passivation layer over the sensor electrodes. 
     
     
       12. The integrated sensor device as claimed in  claim 11 , wherein the porous oxide is on the passivation layer, and the MOS circuits detect changes in a fringe field between the sensor electrodes. 
     
     
       13. The integrated sensor device as claimed in  claim 11 , wherein the passivation layer is of Si 3 N 4  composition. 
     
     
       14. The integrated sensor device as claimed in  claim 11 , wherein the passivation layer is recessed over the sensor electrodes. 
     
     
       15. The integrated sensor device as claimed in  claim 11 , wherein the passivation layer is recessed over the sensor electrodes, and wherein the sensor porous material is in the recess. 
     
     
       16. The integrated sensor device as claimed in  claim 11 , further comprising etch stop layers between the interconnect levels, and the passivation layer is of a same composition as the etch stop material.